Shunshin evades Kamui, and multiple FRS tear Susanoo and the Sharingan Duo apart. S2 is only easier since Senjutsu KCM FRS>>>KCM FRS just how a SM FRS>>>Base FRS or a KCM FRS>>>Base FRS.
S2 is a god stomp. Hiraishin foils Kamui and shits on Kakashi, and it lets him shit on Itachi by either warping him out of Susanoo, warping his Susanoo away, or by breaking through with multiple Bijuu Rasengan, assuming he can use the jutsu.